Question 451. 1.  A 6-pole, 3-phase, 60 Hz induction motor runs at 1000 rpm developing maximum torque. Rotor resistance per phase is 1.2 ohms. Neglecting stator impedance, then for developing maximum torque, the external resistance to be connected in series with each rotor phase will be

Question 452. 2. . The capacitor-start single-phase induction motors develop much larger starting torque in comparison with the "split-phase" motors, because the use of capacitors in the auxiliary winding

Question 453. 9.  For a rotor-fed 3-phase induction motor, the absolute speed of the rotating magnetic field in space is

Question 454. 0.  A 3-phase induction motor has a full-load slip of 3 per cent at normal voltage. Which one of the following will be the value of the slip of the motor if it develops the same torque theoretically while operating at 110 per cent of its normal voltage?

Question 455. 3. The rotor of a three-phase induction machine is replaced by a rotor with a commutator type winding having no external connection between the brushes. The stator is supplied from a balanced three-phase source and the rotor is driven at twice the synchronous speed in the direction opposite to the stator mmf. The frequency of the emf induced between consecutive brushes will be (f is the supply frequency)

Question 456. 4.  Which one of the following relations between starting torque 'Ts' and maximum torque 'Truax' is correct? ('a' is the ratio of rotor resistance to standstill rotor reactance)Ts

Question 457. 5.  For a given load, the speed of shaded-pole single-phase induction motor fluctuates slightly because

Question 458. 6.  Two separate induction motors having 6 poles and 4 poles are cascaded 3-phase, 400 V, 60 Hz is the supply to the motors. The synch ronous speeds (in rpm) of cascaded set will be

Question 459. 8.  3-phase delta connected squirrel cage induction motor has a starting current of IA and a starting torque of TA at rated voltage. If the starting current and starting torque while the motor is started through star-delta starter and auto-transformer (with 60% voltage) starter alternatively, are Iy and Ty and 'auto and Tauto respectively, then autoIauto is equal to

Question 460. 0.  In the slip power recovery method of speed control of a 3-phase wound rotor induction motor, to operate it in the subsynchronous region of speed, a voltage has to be injected across the rotor terminals